Small Engines (Lawn Mowers, etc.): b&s 14hp back fires as if out of time ,will not start, air gap, valve timing

Question
B&S 14 ohc rider mower had broken piston,repaired and now it will not start, it acts as if it is out of time and we set the valves as we read but still will not start , it back fires thru the carb . what are we doing wrong . ready to pull hair out

Answer
A couple of things that will cause backfiring through the carb are incorrect valve timing and incorrect ignition timing.  It's unlikely your ignition timing is off as the flywheel key and the air gap between the coil and the flywheel determine this (no other adjustment).  You can probably guess what I'm going to recommend....the valve timing is off and needs to be confirmed.  Hope this helps.